On 8/25/15 6:05 PM, Peter Zijlstra wrote:
On Tue, Aug 25, 2015 at 03:59:54PM +0800, Wanpeng Li wrote:
+++ b/kernel/cpuset.c
@@ -2376,8 +2376,12 @@ void cpuset_cpus_allowed(struct task_struct *tsk, struct
cpumask *pmask)
void cpuset_cpus_allowed_fallback(struct task_struct *tsk)
{
+ unsigned long flags;
+
rcu_read_lock();
+ raw_spin_lock_irqsave(&tsk->pi_lock, flags);
do_set_cpus_allowed(tsk, task_cs(tsk)->effective_cpus);
+ raw_spin_lock_irqsave(&tsk->pi_lock, flags);
rcu_read_unlock();
Aside from the double lock thing that was already pointed out, I think
this is wrong, because the select_task_rq() call can already have
pi_lock held.
Taking it again would result in a deadlock.
Consider for instance:
try_to_wake_up()
raw_spin_lock_irqsave(->pi_lock)
select_task_rq()
select_ballback_rq()
cpuset_cpus_allowed_fallback()
raw_spin_lock_irqsave(->pi_lock)
The problem is with the migration path and should be fixed there.
Indeed, it should be fixed in migration path. I will try to fight it out
and post a patch. :)
Regards,
Wanpeng Li
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